Solenoid valve

ABSTRACT

A solenoid valve appropriately used for pressure control of various fluids, or the like is concerned, and a solenoid valve is provided, which achieves improvement in sliding property of a plunger and is excellent in control characteristics. More specifically, a plunger  1  is substantially cylindrical-shaped and slidably supported at its outer peripheral side by a sleeve, the plunger being provided with a large-diameter portion  1   a,  which constitutes a sliding portion, the large-diameter portion  1   a  being alternately provided with a plurality of convex surface portions  1   d  and a plurality of groove portions  1   e  and having a cross sectional shape like petals.

TECHNICAL FIELD

[0001] The present invention relates to a solenoid valve used suitablyfor pressure control of various fluids or the like.

BACKGROUND ART

[0002] Conventionally, a solenoid valve of this type is shown in, forexample, FIG. 8. FIG. 8 is across sectional view showing a schematicconstruction of a solenoid valve of the conventional art.

[0003] A solenoid valve 200 comprises a solenoid section 200A and avalve section 200B.

[0004] Here, the valve section 200B comprises a spool valve constructedsuch that since an opening area of the valve is varied according to astroke of a spool, a solenoid controls a stroke amount of the spool tobe able to control an amount of inflow and an amount of outflow.

[0005] The solenoid section 200A generally comprises a coil 203, aplunger 201 adapted to be magnetically attracted by a center post 202upon energization of the coil 203, and a rod 204 connected to theplunger 201 to transmit driving of the plunger 201 to the valve section200B (concretely, the spool).

[0006] Also, provided are a first bearing 205 and a second bearing 210for increasing a coaxiality of the plunger 201 and the rod 204, whichreciprocate, a sleeve 206 supporting the plunger 201 and so on, an upperplate 207 and a lower plate 209, which form a magnetic path, a casing208, and the like.

[0007] Here, the plunger 201 is configured to be positioned in adirection away from the center post 202 in a normal state, that is, astate, in which electricity is not fed to the coil 203.

[0008] In addition, generally, a biasing member such as springs, or thelike, biases the plunger 201 in a direction away from the center post202. In an example shown, a spring for biasing the spool toward thesolenoid section 200A is provided whereby the plunger is spaced awayfrom the center post 202 through the spool.

[0009] So, electricity is fed to the coil 203 to thereby form a magneticpath, so that the plunger 201 is magnetically attracted by the centerpost 202.

[0010] Accordingly, magnetic forces can be controlled according to amagnitude of current fed to the coil 203, so that an amount of movementof the plunger 201 is controlled by controlling balancing associatedwith the biasing member such as springs, or the like, whereby it ispossible to control an amount of stroke of the spool, thus enablingcontrolling a flow rate of a fluid, pressure control, such as hydrauliccontrol, of various fluids, or the like.

[0011] Here, coaxiality is cited as a fundamental performance generallyrequired for solenoid valves. The reason for this is that with aninadequate coaxiality, a plunger and a rod repeatedly reciprocateobliquely to an axis whereby local abrasion, in which abrasion is partlycaused, is generated to lead to degradation in control characteristics,such as hysteresis, in which a change in characteristics is producedbetween outward way and homeward way, deviation of magnetic flux towarda plunger, or the like.

[0012] Such coaxiality is determined by sizing of respective members,and the more members related to centering, the more propagation of anerror due to dimensional tolerances of the respective members.

[0013] With the solenoid valve 200 shown in FIG. 8, members related tocentering include those members, which abut directly against, orindirectly support the plunger 201, the center post 202, and the rod204, and so nine members comprising the plunger 201, center post 202,and the rod 204 themselves, the first bearing 205, second bearing 210,sleeve 206, upper plate 207, lower plate 209, and the casing 208.

[0014] Accordingly, since dimensions of the nine members must bestrictly managed, a burden for enhancing accuracy in coaxiality issignificant.

[0015] Hereupon, in order to lighten such burden, a construction hasbeen developed, in which a sleeve supporting a plunger serves asbearings for the plunger itself for reduction of the number of membersrelated to centering.

[0016] While a detailed description is omitted, the members related tocentering in this case include five members, that is, a plunger, rod,center post, sleeve, and a rod bearing, so that a burden in dimensionalmanagement decreases and it is possible to attain improvement incoaxiality.

[0017] Also, since the need of bearing structures on both end sides of aplunger as in the arrangement shown in FIG. 8 is obviated, there isproduced an advantage that miniaturization can be achieved in an axialdirection.

[0018] With the solenoid valve thus constructed, it is required that aplunger be excellent in sliding quality relative to an inner peripheryof a sleeve, which serves as a bearing, in order to perform smooth andstable reciprocating motions, and flow passages (oil passages, or thelike) be provided on an outer peripheral surface of the plunger so as toeliminate pressure load on both end sides in an axial direction andprovide a high sliding quality.

[0019] This will be described with reference to FIG. 7. FIG. 7 showsschematic, cross sectional views of a configuration of a plungeraccording to the conventional art ((A) is a cross sectional view as cutthrough an axis, and (B) is a cross sectional view as cut in a directionperpendicular to the axis (AA cross section in (A) and corresponding toa whole part).

[0020] As shown in the figure, a plunger 301 of the conventional art issubstantially cylindrical-shaped to comprise a large-diameter portion301 a, which slides on an inner periphery of a sleeve, and a groove 301b serving as a flow passage is formed by cutting.

[0021] Thus, the inner periphery of the sleeve and the plunger 301 sliderelative to each other while curved surfaces of substantially the samediameter contact with each other, and a liquid (oil) flows in by way ofthe flow passage, so that it is not subjected to pressure load andsliding is effected while given lubrication by the liquid, thereby it isenabled reciprocating motions suitably.

[0022] Since there is a need of providing a predetermined clearancebetween an inner peripheral diameter of the sleeve and an outerperipheral diameter of the plunger in order to perform a smooth sliding,the plunger is not actually reciprocated while being kept completelycoaxial with the sleeve, but the large-diameter portion 301 a of theplunger and an inner periphery 302 of the sleeve slide while contactingwith each other at one point in a cross section perpendicular to anaxis.

[0023] In the case of the conventional art, however, there is caused thefollowing problem.

[0024] As described above, since the plunger slides relative to thesleeve while contacting with each other at one point in a cross sectionperpendicular to the axis, there is involved a disadvantage that load atthe time of sliding is liable to makes a burden great and a property ofsliding abrasion is made worse.

[0025] Also, since the outer diameter of the plunger and the innerperipheral diameter of the sleeve are of substantially the samedimension, a gap in the vicinity of slide portions is very narrow tocause a problem that when foreign matters (impurities) enter, theyremain to be caught in, thereby making the sliding property worse.

[0026] An object of the invention is to provide a solenoid valve, whichis intended for improvement in sliding property of a plunger andexcellent in control characteristics.

DISCLOSURE OF THE INVENTION

[0027] To attain the object, the invention provides a solenoid valvecomprising a plunger for reciprocation by means of magnetic forcesproduced by excitation means, and a sleeve slidably supporting an outerperiphery of the plunger to bear the same, and wherein the sleeve isprovided with an inner peripheral wall surface for the bearing, theinner peripheral wall surface being perpendicular to an axis andcircular-shaped in cross section, and the plunger comprises on an outerperiphery thereof a plurality of convex surface portions in the form ofa curved surface, which has a smaller radius of curvature than adistance between the axis and a surface of the outer periphery, theconvex surface portions sliding on the inner peripheral wall surface andextending in an axial direction, and a plurality of grooves eachprovided between adjacent convex surface portions and forming an axiallyextending flow passage.

[0028] Accordingly, since a curved surface having a smaller radius ofcurvature than a distance between the axis and a surface of the outerperiphery, that is, a curved surface having a smaller radius ofcurvature than a diameter of the inner periphery of the sleeve effectssliding, two adjacent convex surface portions effect sliding for thereason that sliding with only one convex surface portion is unstable.That is, sliding is effected not at one point as in the conventional artbut at two points in a cross section perpendicular to an axis. Thereby,since a load is dispersed in two-point contact as compared withone-point contact, sliding abrasion is decreased.

[0029] Also, since a curved surface having a smaller radius of curvaturethan a diameter of the inner periphery of the sleeve effects sliding,gaps near the sliding portions can be made comparatively large to makeentry of a fluid easy, so that the lubricating property is made good andin the case where foreign matters enter, they become easy to escape intothe flow passages.

[0030] Preferably, the convex surface portions are distributed equallyin a circumferential direction and provided in an odd number oflocations.

[0031] Accordingly, since the convex surface portions and the grooveportions are disposed in a positional relationship that is symmetricalwith an axis interposed therebetween, an outer peripheral surface on anopposite side in a middle position (groove portion) between the twoconvex surface portions with an axis therebetween is made furthest fromthe inner periphery of the sleeve in a state, in which adjacent convexsurface portions effect sliding, and the portions constitute the convexsurface portions whereby backlash can be suppressed.

[0032] Preferably, cross sections of flow passages formed by the groovesand the inner peripheral wall surface to be perpendicular to the axisare set to dimensions and a shape to cover dimensions and a shape of amesh of a filter, by which impurities contained in a fluid flowing intoa body of the solenoid valve are removed outside the body of thesolenoid valve before inflowing.

[0033] Accordingly, a size of impurities contained in a fluid flowinginto a body of the solenoid valve is restricted by the filter to a size,which is permitted to pass through the mesh of the filter. Since crosssections of the flow passages are dimensioned and shaped to coverdimensions and a shape of the mesh of the filter, plugging of impuritiesin the flow passages is obviated.

[0034] Preferably, the convex surface portions and the grooves providedon the outer periphery of the plunger are obtained by die forging, theplunger is provided on an end surface, which is opposed in a directionof pressurization at the time of die forging, with an inwardly recessedrecess, and a bottom surface of the recess constitutes that portion,which is pressed by an ejector pin in order that a plunger body is takenout from a forging die after the die forging.

[0035] Accordingly, even if burr is generated on that portion (portionbeing pressed), which is pressed by an ejector pin when a plunger bodyis pushed out from a forging die by the ejector pin, burr is generatedonly at a bottom surface of the recess, so that an entire length of theplunger is not affected thereby.

[0036] Also, the invention provides a solenoid valve comprising aplunger for reciprocation by means of magnetic forces produced byexcitation means, and a sleeve slidably supporting an outer periphery ofthe plunger to bear the same, and wherein the sleeve is provided with aninner peripheral wall surface for the bearing, the inner peripheral wallsurface being perpendicular to an axis and circular-shaped in crosssection, and a portion of the plunger sliding on the inner peripheralwall surface has a cross section perpendicular to an axial direction andhaving an outer peripheral shape of a polygon.

[0037] Here, “polygon” includes the case where respective corners assumea R-shape,

[0038] With the configuration, the inner peripheral wall surface of thesleeve having a circular-shaped cross section slidably supports theplunger having a cross section, of which an outer peripheral shape ispolygonal. Accordingly, since the plunger is made unstable when slidingonly at one corner, sliding is effected at two adjacent corners. Thatis, sliding is effected not at one point as in the prior art but at twopoints in a cross section perpendicular to an axis. Thereby, since aload is dispersed in two-point contact as compared with one-pointcontact, sliding abrasion is decreased.

[0039] Also, since sliding is effected at corners, gaps near the slidingportions can be made comparatively large to make entry of a fluid easy,so that the lubricating property is made good and in the case whereforeign matters enter, they become easy to escape into the flowpassages.

[0040] Preferably, the outer peripheral shape is a polygon having an oddnumber of vertices. In particular, the outer peripheral shape ispreferably a substantially regular nonagon.

[0041] Accordingly, the corners and the planar surface portions on theouter periphery of the plunger are put in a positional relationship thatis symmetrical with respect to an axis, so that is possible to reducebacklash. Also, flow passages formed by the planar surface portions onthe outer periphery of the plunger and the inner peripheral wall surfaceof the sleeve can be set to an appropriate magnitude in cross sectionalarea in the case where taking account of balancing between feeding of amagnetic path and discharge of foreign matters. In the case of cutting aplunger, planar surface portions of the plunger are chucked. It ispreferable to effect three-point chucking, in which case it is necessaryto make the outer peripheral shape a polygon (regular polygon), whichhas vertices being a multiple of 3 in number, and a regular nonagonpreferably meets such condition.

[0042] Preferably, cross sections of flow passages formed by planarportions on the outer periphery of the plunger and the inner peripheralwall surface of the sleeve to be perpendicular to the axial directionare set to dimensions and a shape to cover dimensions and a shape of amesh of a filter, by which impurities contained in a fluid flowing intoa body of the solenoid valve are removed outside the body of thesolenoid valve before inflowing.

[0043] Accordingly, a size of impurities contained in a fluid flowinginto a body of the solenoid valve is restricted to a size, which ispermitted to pass through the mesh of the filter. Since cross sectionsof the flow passages are dimensioned and shaped to cover dimensions anda shape of the mesh of the filter, plugging of impurities in the flowpassages is obviated.

BRIEF DESCRIPTION OF THE DRAWINGS

[0044]FIG. 1 is a schematic, cross sectional view showing a constitutionof a solenoid valve according to an embodiment of the invention;

[0045]FIG. 2 are schematic, cross sectional views of a configuration ofa plunger according to a first embodiment of the invention;

[0046]FIG. 3 is a diagrammatic view showing a state of sliding portionsbetween a plunger and an inner periphery of a sleeve;

[0047]FIG. 4 is a diagrammatic view showing a configurational example ofa groove provided on the plunger;

[0048]FIG. 5 is a schematic, cross sectional view showing a plungeraccording to a second embodiment of the invention;

[0049]FIG. 6 is a diagrammatic view showing a part of the manufacturingprocess of a plunger according to embodiments of the invention;

[0050]FIG. 7 are schematic, cross sectional views of a configuration ofa plunger according to the conventional art; and

[0051]FIG. 8 is a schematic, cross sectional view showing a constructionof a solenoid valve of the conventional art.

BEST MODE FOR CARRYING OUT THE INVENTION

[0052] Preferred embodiments of the invention will be exemplarilydescribed below in detail with reference to the drawings. However, ascope of the invention is not to be limited only to dimensions,materials, configurations, and relative positions of constituent partsdescribed in the embodiments unless otherwise specifically described.

[0053] (First Embodiment)

[0054] A solenoid valve according to a first embodiment of the inventionwill be explained with reference to FIGS. 1 to 5.

[0055]FIG. 1 is a schematic, cross sectional view showing a constitutionof a solenoid valve according to the embodiment of the invention. FIG. 2shows schematic, cross sectional views of a configuration of a plungeraccording to the first embodiment of the invention ((A) is a crosssectional view as cut through an axis, and (B) is a cross sectional viewas cut in a direction perpendicular to the axis (BB cross section in (A)and corresponding to a whole part). FIG. 3 is a diagrammatic viewshowing a state of a plunger and an inner periphery of a sleeve. FIG. 4shows a configurational example of a groove provided on the plunger.FIG. 5 is a diagrammatic view showing a part of the manufacturingprocess of a plunger according to embodiments of the invention.

[0056] A solenoid valve 100 comprises a solenoid section 100A and avalve section 100B.

[0057] H re, the valve section 100B comprises a spool valve constructedsuch that a spool 15 is provided in a valve sleeve 16 to be able toreciprocate therein and since an opening area of a valve formed in thevalve sleeve 16 is varied according to a stroke of the spool 15, asolenoid controls a stroke amount of the spool 15 to be able to controlan amount of inflow and an amount of outflow.

[0058] The solenoid section 100A generally comprises a coil 3, a plunger1 adapted to be magnetically attracted by a center post 2 uponenergization of the coil 3, a sleeve 4 serving as a bearing for theplunger 1, and a rod 7 connected to the plunger 1 to transmit driving ofthe plunger 1 to the spool 15.

[0059] Also, provided are a bobbin 6, around which the coil 3 is wound,a shim 8 for facilitating separation of the plunger 1 from the centerpost 2, a casing 9, a packing 10 for preventing leakage of a fluid to aside of the coil 3 from an interior of the valve section 100B, an upperplate 11, which forms a magnetic path, and a bracket plate 12, whichalso forms a magnetic path and serves to fix a solenoid valve body in apredetermined position.

[0060] Further, provided are a bearing 13 for the rod 7, a spring 14 forbiasing an E-type ring 18 fixed to the spool 15 to thereby bias theplunger 1 in a direction away from the center post 2 through the rod 7together with the spool 15, and a connector 17 provided with terminals17 a for feeding of electricity to the coil 3.

[0061] In addition, the coil 3 and the bobbin 6 are molded to beassembled (Assy) to constitute a mold coil sub-Assy 5.

[0062] Here, the plunger 1 is configured to be positioned in a directionaway from the center post 2 in a normal state, that is, a state, inwhich electricity is not fed to the coil 3, that is, the spring 14 inthe embodiment biases the spool 15 in a direction toward the solenoidsection 100A through the E-type ring 18 whereby the plunger 1 isseparated from the center post 2.

[0063] So, electricity is fed to the coil 3 to thereby form a magneticpath (a magnetic path formed by the casing 9, upper plate 11, plunger 1,center post 2, and the bracket plate 12), so that the plunger 1 ismagnetically attracted by the center post 2.

[0064] Accordingly, magnetic forces can be controlled according to amagnitude of current fed to the coil 3, so that an amount of movement ofthe plunger 1 is controlled by controlling balancing associated with abiasing force produced by the spring 14, whereby it is possible tocontrol an amount of stroke of the spool 15, thus enabling controlling aflow rate of a fluid, pressure control, such as hydraulic control, ofvarious fluids, or the like.

[0065] Here, since the plunger 1 is born by the sleeve 4 in theembodiment, members related to centering include five members, that is,the plunger 1, rod 7, center post 2, sleeve 4, and the rod bearing 13, aburden in dimensional management is comparatively small and it ispossible to attain improvement in coaxiality.

[0066] Also, since the need of bearing structures on both end sides ofthe plunger 1 is obviated, there is produced an advantage thatminiaturization can be achieved in an axial direction.

[0067] Subsequently, a further detailed explanation will be given to theplunger 1.

[0068] The plunger 1 is substantially cylindrical-shaped to permit therod 7 to be fitted into a hole 1 b on an inner peripheral side thereofand to have an outer peripheral side thereof slidably supported by thesleeve 4 as described above, thus a large-diameter portion 1 a, whichconstitutes a slide portion, being provided.

[0069] The large-diameter portion 1 a comprises a plurality of convexsurface portions 1 d and a plurality of groove portions 1 e, as shown inFIG. 2(B), these portions being provided alternately, and has a crosssectional shape like that of petals.

[0070] The convex surface portions id extend axially, and distancesbetween tip ends (most distant from an axis) of the respective convexsurface portions 1 d and then axis are set to be the same.

[0071] Further, the convex surfac portions 1 d assume a shape of asmooth curved surface, and a radius of curvature of outer peripheral,curved surfaces in a cross section perpendicular to the axis is set tobe smaller than distances between the tip ends of the convex surfaceportions 1 d and the axis. Thereby, distances between the tip ends ofthe convex surface portions 1 d and the axis are smaller by an amount ofa clearance than an inner peripheral diameter of the sleeve 4, so thatthe radius of curvature of the outer peripheral, curved surfaces becomesnaturally smaller than the inner peripheral diameter of the sleeve 4.

[0072] For example, it is assumed that distances between the tip ends ofthe convex surface portions 1 d and the axis are 5 mm and a radius ofcurvature in the vicinity of the tip ends of the convex surface portions1 d is 3 mm. In addition, the inner periphery of the sleeve 4 has aradius larger by an amount of a clearance than 5 mm.

[0073] The tip ends of the convex surface portions 1 d are disposedslidably on the inner peripheral surface of the sleeve 4.

[0074] The axially extending groove portions 1 e, respectively, areprovided between the adjacent convex surface portions 1 d, and flowpassages are defined between the groove portions 1 e and the innerperipheral surface of the sleeve 4.

[0075] In the case where the plunger 1 slides on the inner periphery ofthe sleeve 4 in the solenoid valve 100 constructed in the above manner,the plunger 1 is not reciprocated while being kept completely coaxialwith the sleeve 4, since there is provided a clearance for smoothsliding, as described with respect to the conventional art.

[0076] With the embodiment, a radius of curvature (outer peripheraldiameter) of the slide surface portions is not substantially the same asa radius of curvature (inner peripheral diameter) of the innerperipheral surface of the sleeve unlike the conventional art and aradius of curvature of the convex surface portions 1 d, which constitutethe slide surface portions, is smaller than a radius of curvature (innerperipheral diameter) of the sleeve 4, so that a very unstable slidingonly at one point in a cross section perpendicular to an axis is notactually effected, and the adjacent convex surface portions 1 d performsliding while contacting at two points as shown in FIG. 3(A).

[0077] Accordingly, load is dispersed as compared with the case ofcontact at one point in a cross section perpendicular to an axis as inthe conventional art, and a burden of load on the sliding portions isreduced, so that a property of sliding abrasion is improved.

[0078] Also, like the conventional art, the curved surfaces slide oneach other while contacting with each other and a liquid (oil) flows inby way of flow passages, so that it is not subjected to pressure load,and sliding is effected while given lubrication by the liquid; therebyit is enabled reciprocating motions suitably.

[0079] Also, with the embodiment, a radius of curvature of the convexsurface portions 1 d is smaller than a radius of curvature (innerperipheral diameter) of the sleeve 4, and so a fluid easily flows ontothe sliding portions from flow passages formed by the groove portions 1e to make lubrication excellent as compared with the conventional art,thus improving the sliding property.

[0080] Further, a radius of curvature of the convex surface portions 1 dis smaller than a radius of curvature (inner peripheral diameter) of thesleeve 4, and gaps in the vicinity of the sliding portions are large ascompared with the conventional art, so that even when foreign matters(impurities) enter in the vicinity of the sliding portions, foreignmatters easily escape into flow passages, thus enabling preventing thatdegradation in the sliding property, which is caused by the foreignmatters.

[0081] In this manner, the plunger is improved in sliding property, sothat fluid controllability such as hydraulic control, or the like, isimproved.

[0082] An explanation will be given below to a preferred, concreteexample.

[0083] It is preferable that the convex surface portions 1 d bedistributed equally in a circumferential direction and provided in anodd number of locations.

[0084] Thus, being distributed equally and provided in an odd number oflocations, the convex surface portions 1 d and the groove portions 1 eare disposed in a positional relationship that is symmetrical with anaxis interposed therebetween (see FIG. 2(B)).

[0085] Accordingly, the plunger 1 slides with the adjacent convexsurface portions 1 d making contact at two points and an outerperipheral surface opposed to the groove portion 1 e in a middleposition between the two points with an axis therebetween is madefurthest from an inner periphery of the sleeve, so that such portion ismade a convex surface portion 1 d whereby there is produced an effect ofmaking the gap as small as possible to suppress backlash.

[0086] Also, while FIG. 2(B) shows an example, in which the grooveportions 1 e have a curved surface connected smoothly to the convexsurface portions 1 d and having a radius of curvature R2 equal to aradius of curvature R1 of the convex surface portions 1 d, the grooveportions are not limited thereto but may be rectangular-shaped grooveportions 1 g shown in FIG. 4(A), or triangular-shaped groove portions 1h shown in FIG. 4(B).

[0087] Here, it is desired that a cross section of flow passagesperpendicular to an axis defined by the groove portions 1 e and an innerperiphery of the sleeve 4 be dimensioned and shaped in such a manner toprevent impurities contained in a fluid flowing through the flowpassages from being caught.

[0088] In the case where, for example, a filter for removal ofimpurities contained in a fluid is installed in a flow passage forintroducing the fluid into the solenoid valve 100 in order to meet thedesire, only impurities smaller than a mesh of the filter are containedin a fluid flowing into the solenoid valve 100.

[0089] Accordingly, dimensions and a shape of a cross section of theflow passages perpendicular to an axis are made to cover dimensions anda shape of a mesh of the filter whereby it is possible to preventimpurities from being caught and plugged in the flow passages defined bythe groove portions 1 e and the inner periphery of the sleeve 4.

[0090] Accordingly, it is possible to maintain a stable slidingproperty.

[0091] Subsequently, an explanation will be give to a preferred exampleof application of the solenoid valve 100 according to the embodiment.

[0092] In engines of automobiles or the like, in which cam shafts arerotated to open and close air supply and exhaust valves of the engine,it is possible to enhance fuel efficiency and obtain a high exhaust gaspurification by appropriately controlling timing of the valves accordingto an operating state (high speed/low speed).

[0093] Such control of valve timing can be performed by shifting camshafts in a direction of rotation for phase change, and a technique ofperforming such shifting with solenoid valves has been known as a knowntechnique.

[0094] Here, hydraulic control with the use of solenoid valves isperformed to shift cam shafts in a direction of rotation, and it iscommon that the a solenoid valve is mounted on a path of a flow passagefor an engine oil in terms of an installation space, or the like, and anengine oil is made use of.

[0095] Conventionally, a solenoid valve for performing on-off control isused to perform control by two states at high speed and at low speed. Inrecent years, solenoid valves capable of linear control have been usedto perform a highly precise control.

[0096] Here, it becomes possible to preferably use the solenoid valveaccording to the embodiment of the invention as such linear controlsolenoid valve for valve timing control (VTC).

[0097] Hereupon, in the case of making use of an engine oil as describedabove, foreign matters such as iron powder, or the like are largelycontained in an engine oil and so a fluid in a comparatively badcondition is used. Since the solenoid valve according to the embodimentpermits foreign matters to flow into the flow passages to be excellentin sliding property, it can be preferably made use of even under suchbad condition.

[0098] Subsequently, an explanation will be give to a method ofmanufacturing a plunger 1, which constitutes the solenoid valve 100according to the embodiment, with reference to FIG. 6.

[0099] The plurality of convex surface portions 1 d and the plurality ofgroove portions 1 e on the large-diameter portion 1 a of the plunger 1can be fabricated in die forging by clamping with forging dies 50, 51and pressurization in a direction indicated by an arrow P in the figure.In addition, the forging die 51 is indicated by dotted lines for theexplanation of subsequent manufacturing processes.

[0100] Also, 1 f in the figure denotes a portion being cut in a cuttingprocess after the die forging.

[0101] Here, in order to take out a body of the plunger 1 from the dieafter the die forging is carried out, it is necessary to use an ejectorpin 52 to press (strike) an end surface on an opposite side in thedirection of the arrow P after the forging die 51 is removed.

[0102] Here, the plunger according to the embodiment is provided, on theend surface thereof on the opposite side in the direction of the arrowP, with a recess 1 c, which is recessed inwardly of a tip end surface,and a bottom surface of the recess 1 c serves as a portion being pressedby the ejector pin 52.

[0103] Thereby, while burr is generally generated when pressed by theejector pin 52, the bottom surface of the recess 1 c serves as a portionbeing pressed in the embodiment, so that burr B1 and burr B2 aregenerated only in the recess as shown in an enlarged view (P) in FIG. 6,and so have no influence on an entire length of the plunger 1.

[0104] Accordingly, an entire length of an plunger must be strictlycontrolled in the case where a stroke of the plunger has an influence oncontrol of a solenoid valve, and so it is normally necessary toimplement a cutting process for the deburring process in the case whereburr has an influence. Since burr has no influence on an entire lengthof a plunger in the embodiment, such processing step is dispensed with.

[0105] (Second Embodiment)

[0106] An explanation will be given to a solenoid valve according to asecond embodiment of the invention with reference to FIG. 5. Since thesolenoid valve according to the second embodiment of the invention isdifferent only in the constitution of a plunger from the firstembodiment, a detailed explanation will be given only to a plunger andan explanation for other constitution is omitted.

[0107]FIG. 5 is a schematic, cross sectional view as cut in a directionperpendicular to an axis of a plunger according to the second embodimentof the invention. In addition, the cross sectional view as cut throughthe axis of the plunger according to the embodiment is similar to FIG.2(A) illustrated in the embodiment. Accordingly, FIG. 5 is a viewcorresponding to the BB cross section in FIG. 2(A).

[0108] A large diameter portion 1′a of the plunger according to theembodiment, which constitutes a portion sliding relative to the sleeve4, has an outer peripheral shape of polygon (regular nonagon in theexample shown) in cross section perpendicular to an axial direction.

[0109] A distance between an axis and a corner 1′d is set to be smallerby a clearance than the inner periphery of the sleeve 4. Accordingly,the corners 1′d are disposed to be able to slide on the inner peripheralsurface of the sleeve 4.

[0110] And flow passages are defined between planar surface portions 1′ebetween the corners 1′d and the inner peripheral surface of the sleeve4.

[0111] The plunger is structured in the above manner, whereby a veryunstable sliding only at one point in a cross section perpendicular toan axis is not actually effected in the same manner as in the firstembodiment, and the adjacent corners 1′d perform sliding whilecontacting at two points.

[0112] Accordingly, load is dispersed as compared with the case ofcontact at one point in a cross section perpendicular to an axis as inthe conventional art, and a burden of load on the sliding portions isreduced, so that a property of sliding abrasion is improved.

[0113] Also, since the corners 1′d slide on the inner peripheral wallsurface of the sleeve 4 in the embodiment, a fluid easily flows onto thesliding portions from flow passages formed between the planar surfaceportions 1′e and the inner peripheral surface of the sleeve 4 to makelubrication excellent as compared with the conventional art, thusimproving the sliding property.

[0114] Further, the corners 1′d are configured to slide on the innerperipheral wall surface of the sleeve 4 and so gaps in the vicinity ofthe sliding portions are large as compared with the conventional art, sothat even when foreign matters enter in the vicinity of the slidingportions, foreign matters easily escape into the flow passages, thusenabling preventing that degradation in the sliding property, which iscaused by the foreign matters.

[0115] In this manner, the plunger is improved in sliding property, sothat fluid controllability such as hydraulic control, or the like, isimproved.

[0116] Also, the cross section assumes a substantially regular polygonand the polygon has an odd number of vertices (substantially regularnonagon in the example shown), whereby the corners 1′d and the planarsurface portions 1′e are disposed in a positional relationship that issymmetrical with respect to an axis.

[0117] Accordingly, the plunger 1 slides with the adjacent corners 1′dmaking contact at two points and so an outer peripheral surface opposedto the planar surface portions 1′e in a middle position between the twopoints with an axis therebetween is made furtherest from the innerperiphery of the sleeve, so that the portions are made the corners 1′dwhereby there is produced an effect of making the gaps as small aspossible to suppress backlash.

[0118] Also, it is desired that the corners 1′d assume a R-shape, and Rmust be appropriate since abrasion is increased when R is made toosmall.

[0119] Subsequently, a detailed explanation will be given to the flowpassages defined between the planar surface portions 1′e and the innerperipheral surface of the sleeve 4.

[0120] Since a magnetic path is formed between the outer peripheralsurface of the plunger and the inner peripheral surface of the sleeve 4,it is desired that spacings between the planar surface portions 1′e andthe inner peripheral surface of the sleeve 4 be as small as possibletaking account of a need for eliminating hindrance in feeding ofmagnetic flux.

[0121] Meanwhile, in order to provide a good sliding property, it isdesired that the flow passages be as large as possible in crosssectional area so that a fluid (oil) is adequate in lubrication andadherence of the oil is not generated.

[0122] Also, dimensions and a shape are desirable, which preventsimpurities contained in a fluid flowing through the flow passages frombeing caught.

[0123] For example, in the case where a filter for removal of impuritiescontained in a fluid is installed in a flow passage for introducing thefluid into the solenoid valve 100, only impurities smaller than a meshof the filter are contained in the fluid flowing into the solenoid valve100. Accordingly, dimensions and a shape of a cross section of the flowpassages perpendicular to an axis are made to cover dimensions and ashape of the mesh of the filter whereby it is possible to preventimpurities from being caught and plugged in the flow passages.

[0124] In view of the above points, there is a need of settingdimensions and a shape of the flow passages. In addition, since thecross sectional shape assumes a regular polygon in the embodiment,dimensions and a shape of the flow passages are mainly determineddepending upon which regular polygon is adopted, and a R-dimension ofthe corners.

[0125] Also, it is desired that the plunger in the embodiment be formedby drawing. Thereby, there is produced an advantage that the slittingwork or the like as in the conventional art is dispensed with.

[0126] Also, it is possible to form the plunger by the cutting work.Here, in the case where the cutting work is carried out, chucking mustbe performed for fixation of the plunger, and the planar surfaceportions 1′e must be fixed so as not to cause scratch on the corners1′d, which constitute the sliding portions, due to chucking.

[0127] Here, since three-point chucking (three pawls in 120-degreedirections) is suited to accurate processing, the cross sectionperpendicular to the axis must assume an outer peripheral shape of apolygon (regular polygon) having vertices in number of a multiple of 3.

[0128] As described above, it is necessary to take into considerationthat the cross section of the plunger perpendicular to the axis shouldassume an outer peripheral shape of a polygon having an odd number ofvertices in terms of prevention of backlash, the flow passages should bemade appropriate in magnitude of a cross sectional area in terms offeeding of magnetic flux and lubrication, and a regular polygon havingvertices in number of a multiple of 3 should be adopted in terms of thecutting work.

[0129] In view of these points, it is optimum to adopt a substantiallynonagon.

[0130] Also, while the above condition necessarily determines a setrange of R in the corners 1′d, abrasion is increased when R is made toosmall, and so it is desired that R be set to be maximum in a rangemeeting the above condition.

[0131] Industrial Applicability

[0132] As described above, the invention provides the plurality ofconvex surface portions and the plurality of groove portions on theouter periphery of the plunger, so that since the plunger slidesrelative to the inner peripheral surface of the sleeve at two points ina cross section perpendicular to the axis, a burden of load on thesliding portions is reduced and a property of sliding abrasion and thecontrol characteristics is improved.

[0133] Also, since the curved surfaces having a smaller radius ofcurvature than the diameter of the inner peripheral surface of thesleeve slide, gaps in the vicinity of the sliding portions can be madecomparatively large to make entry of a fluid easy to provide a goodlubrication, and since foreign matters easily escape into the flowpassages when foreign matters enter, the sliding property is improvedand the control characteristics is improved.

[0134] When the convex surface portions are distributed equally in acircumferential direction and provided in an odd number of locations, itis possible to suppress backlash.

[0135] When dimensions and a shape of a cross section of the flowpassages, which are defined between the grooves and the inner peripheralwall surface, perpendicular to an axis are set to cover dimensions and ashape of a mesh of the filter for removal of impurities contained in afluid, it is possible to maintain a stable sliding property withoutplugging of impurities in the flow passages.

[0136] When a recess inwardly recessed is provided on the end surface ofthe plunger on an opposite side in a direction of pressurization at thetime of die forging and the bottom surface of the recess is made aportion being pressed by an ejector pin so that the plunger body istaken out of the forging die after the die forging, burr has noinfluence on an entire length of a plunger even when burr is generatedby the ejector pin, and a stable control is enabled without the need ofthe cutting process.

[0137] Also, even in the case where an outer peripheral shape of a crosssection of the plunger perpendicular to the axis is made a polygon, theplunger slides relative to the inner peripheral surface of the sleeve attwo points in a cross section perpendicular to the axis, so that aburden of load on the sliding portions is reduced to improve a propertyof sliding abrasion and the control characteristics is improved.

[0138] Also, since sliding is effected at the corners, gaps in thevicinity of the sliding portions can be made comparatively large to makeentry of a fluid easy to provide a good lubrication, and since foreignmatters easily escape into the flow passages when foreign matters enter,the sliding property is improved and the control characteristics isimproved.

[0139] When the outer peripheral shape assumes a substantially nonagon,the corners and the planar surface portions are put in a positionalrelationship that is symmetrical with respect to an axis, so that it ispossible to reduce backlash and to set the flow passages to anappropriate magnitude in cross sectional area, and it is possible toeffect three-point chucking in the case of the cutting work.

[0140] When dimensions and a shape of a cross section of the flowpassages, which are defined by the planar surface portions on the outerperiphery of the plunger and the inner peripheral wall surface of thesleeve, perpendicular to an axis are set to cover dimensions and a shapeof a mesh of the filter for removal of impurities contained in a fluid,it is possible to maintain a stable sliding property without plugging ofimpurities in the flow passages.

1. A solenoid valve comprising a plunger for reciprocation by means ofmagnetic forces produced by excitation means, and a sleeve slidablysupporting an outer periphery of the plunger to bear the plunger, andwherein the sleeve is provided with an inner peripheral wall surface forthe bearing, a cross section of the inner peripheral wall surface beingperpendicular to an axis is circular-shaped, and the plunger compriseson an outer periphery thereof a plurality of convex surface portions inthe form of a curved surface, which has a smaller radius of curvaturethan a distance between the axis and a surface of the outer periphery,the convex surface portions sliding on the inner peripheral wall surfaceand extending in an axial direction, and a plurality of grooves eachprovided between adjacent convex surface portions and forming an axiallyextending flow passage.
 2. The solenoid valve according to claim 1,wherein the convex surface portions are distributed equally in acircumferential direction and provided in an odd number of locations. 3.The solenoid valve according to claim 1, or 2, wherein cross sections offlow passages formed by the grooves and the inner peripheral wallsurface to be perpendicular to the axis are set to dimensions and ashape to cover dimensions and a shape of a mesh of a filter, by whichimpurities contained in a fluid flowing into a body of the solenoidvalve are removed outside the body of the solenoid valve beforeinflowing.
 4. The solenoid valve according to claim 1, 2, or 3, whereinthe convex surface portions and the grooves provided on the outerperiphery of the plunger are obtained by die forging, the plunger isprovided on an end surface, which is opposed in a direction ofpressurization at the time of die forging, with an inwardly recessedrecess, and a bottom surface of the recess constitutes that portion,which is pressed by an ejector pin in order that a plunger body is takenout from a forging die after the die forging.
 5. A solenoid valvecomprising a plunger for reciprocation by means of magnetic forcesproduced by excitation means, and a sleeve slidably supporting an outerperiphery of the plunger to bear the plunger, and wherein the sleeve isprovided with an inner peripheral wall surface for the bearing, a crosssection of the inner peripheral wall surface being perpendicular to anaxis is circular-shaped, and a portion of the plunger sliding on theinner peripheral wall surface has an outer peripheral shape of a polygonin cross section perpendicular to an axial direction.
 6. The solenoidvalve according to claim 5, wherein the outer peripheral shape is apolygon having an odd number of vertices.
 7. The solenoid valveaccording to claim 5, wherein the outer peripheral shape is asubstantially nonagon.
 8. The solenoid valve according to claim 5, 6, or7, wherein cross sections of flow passages formed by planar portions onthe outer periphery of the plunger and the inner peripheral wall surfaceof the sleeve to be perpendicular to the axis are set to dimensions anda shape to cover dimensions and a shape of a mesh of a filter, by whichimpurities contained in a fluid flowing into a body of the solenoidvalve are removed outside the body of the solenoid valve beforeinflowing.